This invention relates to a weighing system wherein weight values from respective ones of a plurality of weighing machines containing articles to be weighed are combinatorially processed to obtain a combination of weighing machines giving a combination of articles having a total weight value within preset allowable limits, followed by discharging the articles from the combination of weighing machines obtained. More particularly, the invention relates to a weighing system of the type described wherein a predetermined weighing machine is compelled to participate in the combinatorial processing.
A combinatorial weighing system which is known in the art includes a plurality of weighing machines and a control apparatus for performing combinatorial computations based on weight values from respective ones of the weighing machines, each of which contains a supply of articles to be weighed. The control apparatus computes combinations of the weight values produced by the weighing machines, obtains a combination (referred to as the "optimum combination") the total weight of which is equal to a target weight value or closest to the target weight value within preset allowable limits, discharges the articles from the machines belonging to the combination obtained, subsequently replenishes the weighing machines which have discharged their articles, with articles in order to prepare for the next weighing cycle, and subsequently repeats the foregoing steps to perform weighing automatically.
In the combinatorial weighing system of the above-described type, there are instances where certain weighing machines are not selected, and hence are not permitted to discharge their articles, even over an extended period of time. For example, if we assume that half of the total number of weighing machines are selected each time, then the probability of a weighing machine being selected each time should be 50% (one out of two). Accordingly, the probability of a weighing machine not being chosen in, say, five consecutive selection cycles is 3.125% (one out of 32), so that we would expect a given weighing machine to be chosen within the five consecutive cycles. In actuality, however, we find that, depending upon the weight of the articles delivered to the weighing machines, a given weighing machine or machines may not be selected over a great many cycles. When a weighing machine is not selected for a prolonged period of time, certain problems arise as will now be described.
(1) One problem involves the combinatorial weighing of frozen foods or foods that tend to spoil easily. Prolonged residence in a weighing machine due to non-selection of the weighing machine over an extended period of time will allow the surface ice on such articles to thaw or result in spoilage. The end result in either case is a product of diminished quality.
(2) A combinatorial weighing system is arranged in such a manner that articles are supplied from a dispersing table to each of a plurality of radial troughs corresponding to the weighing machines, the articles are fed from the troughs to corresponding pool hoppers and then from the pool hoppers to corresponding weighing hoppers for respective ones of the weighing machines. When articles are discharged from a weighing machine selected by combinatorial processing, the weighing machine is resupplied with articles from the corresponding pool hopper, after which the pool hopper is in turned supplied with articles from the corresponding radial trough. If a weighing machine fails to be selected over an extended period of time, therefore, the corresponding pool hopper will not be supplied by its radial trough, but the trough will be supplied with articles from the dispersing table each time a combinatorial processing cycle is executed. Eventually, the radial trough will overflow.
(3) Certain kinds of articles tend to become attached to a weighing machine when the articles reside in the weighing machine for a prolonged period. This results in a weighing error.